Electrical network



June 20, 1933. AGUlRRE 1,914,629

ELECTRICAL NETWORK Filed Oct. 28, 1950 2 Sheets-Sheet l NETWORK INVENTORMAXIMO AGUIRRE June 20 1933. M. AGUERRE 199141529 ELECTRICAL NETWORKFiled Oct. 28, 1930 2 Sheets-Sheet 2 d BASS TREBLE PASS PASS l1 9f u 5 68 a CONTROL CQNTROL i 7 ID WU g 2 NETWORK INVENTQR:

MAXIMO AGUIRRE ATTORNEY.

Patented June 2t), 1933 PATENT OFFICE IVIAXIMO AGUIRRE, OF COTATI,CALIFORNIA ELECTRICAL NETWORK Application filed. October 28, 1930.

This application relates generally to electrical networks such as areutilized for repeating electrical current variations of voicefrequencies. It has particular application to 55 vacuum tube or electronrelay amplifier systems, such as are utilized in connection withbroadcast radio receivers electrical phonographs, talking moving pictureapparatus, and the like, where the quality of the reproduced ortranslated sound is of importance.

In audio frequency amplifying systems it is common for the overallcharacteristic performance curve to drop off for certain frequencieswithin th range of audibility, due

5 to various imperfections. As a result the translation of the currentvariations into sound does not give faithful reproduction. In othersystems in which the amplifiers may have high fidelity, the translatedsound may not give proper tonal efiects due to imperfections in theinput modulations, as for eX- ample where microphone or sound recorddoes not have high fidelity with respect to the original sound waves, orwhere a loud speaker or other translator connected to the output isdefective.

It is an object of the present invention to devise an electrical networkand method of utilizing the same whereby the overall characteristics ofan audio frequency amplifying system with which the invention isemployed, can be modified or compensated to secure better qualityreproduction. I It is a further object of the invention to devise anelectrical network of the above character having provision whereby thenormal repeatin characteristics of the amplifying system with which theinvention is employed can be modified by compensating gains for certainfrequencies, which are at the will of the operator.

It is a further object of the invention to eliminate or minimize motorboating in an electrical network of the above character.

5 Further objects of the invention will ap- Serial No. 491,703.

Fig. 1 is a circuit diagram illustrating an electrical networkincorporating the present invention.

Fig. 2 is a view illustrating the network of Fig. 1 diagrammatically.

Fig. 3 illustrates the electrical network of Fig. 1 applied to an audiofrequency amplifying system having transformer coupling.

Fig. i is a circuit diagram illustrating the electrical network of Fig.1 applied to an audio frequency amplifying system having resistancecoupling.

The nature of the invention can be best understood by referring first todiagrammatic *ig. 2. In this instance I have indicated an electricalnetwork having an input 1 and an output 2. Connected serially betweenthe input and output, there is a gain reducer 3 and an amplifier l.Likewise associated with the input and output, there are two shunt pathsfor repeating audio frequency current varia tions. One shunt path isformed by the unilateral repeating device 5, bass pass 6, and controlmeans 7, while the other path is formed by unilateral repeating device8, treble pass 9, and control means 10. These shunt paths are connectedto the input 1 thru a common phase changer 11, and are connected to theoutput 2 thru the amplifier 4. As will be presently explained, amplifier4 is preferably of the thermionic or electron relay type, and preferablythe unilateral 'repeating devices 5 and 8 are also formed by electronrelays or equivalent means having amplifying characteristics.

It may be briefly pointed out with respect to Fig. 2 that the bass andtreble gains thru the two shunt paths can be adjusted or varied by thedevices 7 and 10, and the combined effect of these two shunt pathshaving their respective gains produce what can be termed a compensatinggain for the network. The gain occurring thru reducer 3 and amplifier 4:to the exclusion of the shunt paths can be termed the normal gain andcan be adjusted to be substantially zero, or at least substantially lessthan the respective gains thru the two shunt paths. Phase changer 11, aswill be later explained, serves to efiect a proper phase change wherebythe current variations repeated by the two shunt paths are in properphase with respect to the current repeated thru reducer 3.

Referring now to the detailed circuit diagram of Fig. 1, the inputcircuit 1 is formed by conductors 21 and 22, While the output 2 isformed byconductors 23 and 24. The gain reducer which is connected totheinput 1 is formed in this instance by resistances 26 and 27, resistance26 being connected across conductors 21 and 22. Conductor 28 isconnected to one terminal of resistance 27 thru condenser 33 and anadjustable tap connection 29 interconnects resistances 26 and 27. Theamplifier designated generally at 4 in Fig. 2 is formed by an electronrelay 31, which can be of the usual three element type, being providedwith a grid or control element, a filament or cathode, and a plate oranode. The grid or control element of electron relay 31 is connected toconductor 28 while the plate or anode is connected to output conductor23. Conductors 22 and 24 of the input and output respectively are shownconnected by the grounded conductor 32, thru condensers 34 and 36respectively, to which the cathode of electron relay 31 is alsoconnected. Assuming that the cathode of electron relay 31 is a filamentor utilizes a filament as a source of heat, this filament can beenergized from a common A-battery circuit such as will be presentlyexplained. In order to properly segregate the grid circuit of electronrelays 31 and 54 from B-battery potentials which may be applied toconductors 21 and 22, blocking condensers 33, 34 and 68 capable ofpassing both bass and treble frequencies are inserted in series withconductors 28, 32 and 20, respectively. Likewise a similar blockingcondenser 36 is inserted between the point of connection with thecathode of relay 31, and the output conductor 24.

It is desirable to so adjust resistors 26 and 27 that the loss ornegative gain effected in the transfer of current variations from theinput 1 to the grid circuit of electron relay 31, is substantially equalto the positive gain effected by repeating the current variations thruelectron relay 31. Therefore, considering that part of the network whichhas been described above with reference to Fig. 1, apart from theremainder of the circuits, the net gain, which is herein referred to asthe normal gain, is substantially zero.

That part of the network which forms a path for repeated currentvariations for effecting a bass gain, includes an electron relay 41, orequivalent unilateral repeating device having amplifyingcharacteristics. A grid leak resistor 42, which is preferably adjustableor variable, is connected across the grid and cathode of the same.Connected in series relationship between the plate or anode of relay 41and conductor 28, there is a condenser 43 capable of passing the lowervoice frequencies,and also a circuit 44 which preferably has bothcapacitative and resistance components. As an example of a suitablecircuit 44, I have shown one side of condenser 47 connected to resistor46 and condenser 43 thru resistance 51. The other side of condenser 47connects to the grounded filament circuit thru conductor 50. Theresistor 51 can be of fixed value. To eifect an adjustment ofcapacitance condenser 47 can be shunted by another condenser 48, uponclosing switch 49. Interposed in series between circuit 44 and conductor28 there is a resistor 53 which is preferably adjustable or variable,and as will be presently explained, adjustments of this resistor serveto adjust the bass gain. The grid of electron relay 41 is connected to.the plate or anode of another electron relay 54, thru a series condenser56. This condenser is of suiiicient capacitance to readily pass thelower or bass frequencies.

That portion of the network serving as a gain path for high or treblevoice frequencies consists of an electron relay 57, having its gridconnected to the grid of relay 41 thru a series condenser 58. Condenser58 is of such capacitance that it will pass relatively high voicefrequencies, or treble frequencies, but will offer relatively highimpedance to bass frequencies. Connected be- F tween the plate or anodeof relay 57 and conductor 28, there is a condenser 59 in seriesrelationship with a relatively fixed resistor 61 and an adjustable orvariable resistor 62. Condenser 59 is likewise of such capacitance thatit will offer relatively high impedance to bass frequencies, but willpass treble frequencies. The capacitance afiorded at this point can beincreased by an additional condenser 63, which can be connected in shuntwith condenser 59 by closing switch 64. Relay 57 is also provided with asuitable grid leak resistor 66, which is connected across the grid andcathode.

Electron relay 54 serves to correct or change the phase angle of currentvariations applied from the input 1 to the grids of electron relays 41and 57. The grid of electron relay 54 is connected to conductor 21 ofthe input 1 thru conductor 20 and series condenser 68 and is alsoconnected to grid leak resist-or 69.

The relays 41 and 57 cause a phase change angle of 180 degrees and therelay 54 also changes the phase angle. Thus current variations ofcompensating gain will be in phase with current variations of normalgain impressed on grid of relay 31.

In order to supply suitable positive B- battery potential to the platesof electron relays 54, 41 and 57, a B-battery conductor 71 is connectedto the plates of these relays thru resistors 72, 73 and 74. Thefilaments of the various electron relays are shown connected to thecommon A-battery circuit 76,

em-n29 one side of which is connected to conductor 32, while the otherside is connected to A- battery terminal 77 thru switch 78. The negativeA-battery terminal 79, which can also serve as a negative B-batteryterminal, is connected to conductor 32. Positive B- battery terminal 81is connected with conductors 24 and 71.

Operation of the network described with reference to Fig. 1 can beexplained as follows: Input 1 is connected to some preceding part of anelectrical system serving as a source of current variations of audiofrequencies. Generally an electron relay ampli tier immediately precedesinput 1 and has its plate circuit connected to conductors 21 and 22.Output 2 is connected to further electrical apparatus which generallyserves to translate the current variations into sound. Usually suchfurther apparatus includes an electron relay amplifier having its inputcoupled to output 2. Current variations impressed upon the input 1 arerepeated thru the reducer afforded by resistors 26 and 2?", and arerepeated by relay 31 to the output 2. As has been previously explained,the gain for this path thru the network, preferably relatively low, asfor example substantially zero, and is termed the normal gain. Currentvariations of all audio frequencies are also impressed upon the grid ofelectron relay 54, the plate of which is coupled to the grids ofelectron relays 41 and 57, thru condensers 56 and 58. Both bass andtreble frequencies are impressed upon the grid of relay 41, due to therelatively large capacitance of condenser 56, while mainly treblefrequencies are impressed upon the grid of relay 57 due to the relatvely small capacitance of condenser 58. Circuit 44 connected between theplate of relay 41 and the grid of relay 31 discriminates againstrelatively high or treble frequencies and in favor of the lower or bassfrequencies. This effect is made possible because of the resistance andcapacitaserves tonarrow the bass gainaor to cause absorption of agreater range of high frequencies, while opening switch 49 serves towiden the bass gain. By varying the value of resistor 53 the volume ofthe bass gain can be varied between practical limits. The effect ofvarying this resistance will be evident when it is considered that it isconnected in series with the connection from the plate of relay 41 tothe grid of relay 31. Therefore a decrease in impedance accompanying adecrease in the res stance of resistor 53 causes an increase in thevolume of bass gain, while increase in the value of resistor 53increases the impedance of the connection between the plate of relay 41to the grid of re lay 31 thus decreasing the volume of bass gain.

As has been previously mentioned, condenser 58 is of such capacitancethat it ofiers relatively high impedance to bass frequencies. Thereforeprincipally treble frequencies are applied to the grid of relay 57. Afurther discrimination in favor of treble frequencies is effected bycondenser 59, which is also of relatively low capacitance. By closingswitch 64 and connecting the shunt of condenser 63 with condenser 59,the range of the treble gain effected by relay 5? can be widened.Adjustments or variations of resistor 62 likewise serve to vary thevolume of treble gain, operating in substantially the same manner asresistor 53 for relay 41. Fixed resistors 46 and 61 in conjunction wththe adjustable or variable resistors 53 and 62, serve the usefulfunction of making the volume control effected by variations ofresistors 53 and 62, more gradually. They also tend to prevent excessgain of relays 41 and 57. Resistor 46 also tends to prevent circuit 44from absorbing some of the higher audio frequencies repeated thru thenormal gar'n, when variable resistance 53 is adjusted to a lower valueto increase bass gain. To further avoid this effect the resistor 51 isconnected in series between resistor 46 and condenser 47 and performsseveral useful results. For example, it permits relay 41 to amplify justenough of the higher audio frequencies to offset the frequenc es whichare otherwise absorbed by circuit 44 as explained. It has also beenfound that the plate or anode of relay 41 tends to have a rectifyingeffect. thus absorbing part of the positive wave of the higher audiofrequencies being repeated thru the normal gain when bass gain is cut inor increased. Since resistor 51 permts relay 4-1 to pass some of thehigher frequencies together with the bass frequencies, such undesiredrectification and absorption are avoided.

Resistor 52, which is preferably adjustable or variable, serves theuseful function of reducing the normal gain when the bass gain isincreased by decreasing the value of resistor 53. This result is madepossible due to the fact that resistors 52 and 53 are in series betweenthe grounded filament circuit of the network and the grid of relay 31.Without such an arrangement the overall. gain of the network wouldbecome too great when bass gain is cut in or increased, th s requiringother adjustments of the network.

Under certain operating conditions when bass gain is cut in orincreased, there will be a tendency for the network to motor boat.

Such a tendency toward motor boating can be eliminated by decreasing thevalue of resistor 42.

lVhen the network is installed with any particular amplifying system, itis evident that certain adjustments must be made, as for exampleadjustments of resistors 42 and 52, in order to insure stability, and inorder to make possible a proper control of the bass and treble gains byvarying resistors 53 and 62. After such adjustments are made for a givenset of operating conditions, resistors 42 and 52 can remain fixed,irrespective of variations in the values of resistors 53 and 62.Likewise resistors 26 and 27 can remain fixed after proper adjustmentsare made.

Assuming now that the network is utilized in conjunction with an audiofrequency amplifying system having a drooping characteristic curve forthe lower or base frequencies, the overall characteristic can becorrected by increasing the bass gain to a proper value, that is bydecreasing the value of resistor 53. Likewise, if the amplifying systemhas a drooping characteristic for the higher frequencies, the overallcharacteristics of the system, that is the system together with thenetwork, can be corrected by cutting in the treble gain. here the audiofrequency current "ariations applied to the amplifying system originatein a sound record, as for example a phonographic or film record,adjustment can be made in the network to compensate for defectiverecording of either high or low frequencies, or both. Likewisecompensating ad ustments of the network can be made to offsetcharacteristics of a loud speaker of poor fidelity supplied 7 soundwaves.

It is evident that my network can be employed in conjunction with audiofrequency amplifying systems having various types of conventionalcouplings. For example, in

- Fi g. 3, my network, which is designated generally at 86, is shownconnected between the stages of an audio frequency amplifier systemhaving transformer coupling. The input to the system is indicated at 87,and is coupled by transformer 88 to the electron relay amplifier 89. Theoutput of amplifier 89 is connected to the input 1 of network 80. Theoutput 2 of network 86 is coupled thru transformer 91, to the input ofthe electron T relay amplifier 92. The output of amplifier 92 suppliesthe loud speaker or equivalent translator 93.

Fig. 4 illustrates my network applied to a resistance coupled audiofrequency amplifying system. In this case the audio frequency currentvariations are applied to the input 90 of the system, and are amplifiedby the electron relay 9?. The output of relay 9'7 connected to the input1 of network So. The output 2 of network 86 has a resistance couplingwith the grid circuit of electron relay amplifier 93. The output ofamplifier 98 is further amplified by electron relay 09, and is'thenapplied to the loud speaker or trans lator 92.

The proper values for the various resistors and condensers utilized inmy network can be readily determined by one skilled in the art for anetwork intended to operate for a certain latitude of conditions. Forexample in one network which I have constructed, resistors 26 and 27have a total value of 25,000 ohms. Grid leak resistor 37 for relay 31has a value of 100,000 ohms. Grid leak resistors 42, 00 and 69 havevalues of 12,000, 30,000 and 100,000 ohms respectively. Plate circuitresisters '42, 73 and Ti have values of 75,000 ohms, 15,000 ohms and30,000 ohms respectivcly. Resistors 46 and 51 have values of 15,000 and1,000 ohms respectively. Resistor 52 has a value of 12,000 olnns andresistor 01 for relay 57 has a value of 25,000 ohms. Variable resistors53 and 62 have a maximum resistance of substantially 2 megohms and aminimum resistance of substantially 10,000 ohms. Condensers 33, 3a, 36,68, 56, i3, each have a capacitance of 1 microfarad. Condensers 47, and48 are of .0 1 and .1 microfarad, capacitance respectively. Condensers58, 59 and 63 are of .006, .001 and .0025 m. f. respectively.

I have previously referred particularly to the use of my network inconjunction with radio broadcast receivers, electrical phonographs, andtalking moving picture apparatus. Other uses which can be mentioned arefor repeater stations of transcontinental wire hookups such as areemployed in connection with raoio broadcasting stations, electricaltranscription broadcasting or recording, and public address systems.

Havin thus described this invention, what l claim and desire to secureby Letters Patent 1s:

1. In an electrical network adapted to repeat current variations ofvoice frequencies, electrically coupled input and output circuits fortransmitting the entire voice range, additional circuits coupled to saidinput and output circuits and including electron relay amplifiers, saidadditional circuits being characterized in that they form separate pathsfor treble and bass frequencies, and means for separately controllingthe respective amplification gains of said additional circuits.

2. In an electrical network adapted to repeat current variations ofvoice frequencies, said network having input and output circuits fortransmitting the entire voice range, a plurality of additional circuitsshunted between said input and outputcircuits, electron relay amplifyingmeans in said additional circuits, means interposed in one of saidcircuits serving to cause the same to offer less impedance to thepassage of treble frequencies than to the passage of bass frequencies,means interposed in another of said additional circuits serving to causethe same to pass bass frequencies in favor of treble frequencies, andmeans for separately controlling the gain in said additional circuits.

3. In an electrical network adapted to repeat current variations ofvoice frequencies, said network having input and output circuits fortransmitting the entire voice range, a plurality of additional circuitsshunted between said input and output circuits, electron relayamplifying means in said additional circuits, means interposed in one ofsaid circuits serving to cause the same to offer less impedance to thepassage of treble frequen cies than to the passage of bass frequencies,means interposed in another of said additional circuits serving to causethe same to pass bass frequencies in favor of treble frequencies, eachof said interposed means consisting of resistance and capacitativecomponents only, and means for separately controlling the gain in saidadditional circuits.

4. In an electrical network adapted to repeat current variations ofVoice frequencies, said network having input and output circuits, meansforming two shunt paths for re peating current variations between theinput and output circuits, one of said paths including in seriesrelationship, an electron relay amplifier, capacitance capable ofpassing bass frequencies, capacitance shunted byresistance, and avariable resistor, the other of said paths including in seriesrelationship another electron relay amplifier, capacitance serving topass principally treble frequencies, and a variable series resistor.

5. In an electrical network adapted to re peat current variations ofvoice frequencies, said network having input and output circuits, anelectron relay amplifier and a gain reducer interposed between saidcircuits, and means forming two shunt paths for repeating currentvariations between the input and output circuits, one of said shuntpaths having a gain for bass frequencies which is greater than thenormal gain thru the reducer and said electron relay amplifier, theother of said paths having a gain for treble frequencies which isgreater than the normal gain thru the reducer and said electron relayamplifier.

6. In an electrical network adapted to repeat current variations ofvoice frequencies,

said network having input and output circuits, an electron relayamplifier and a gain reducer interposed between said circuits, meansforming two shunt paths for repeating current variations between theinput and output circuits, one of said shunt paths having a gain forbass frequencies which is greater than the normal gain thru the reducerand said electron relay amplifier, the other of said paths having a gainfor treble frequencies which is greater than the normal gain thru thereducer and said electron relay amplifier, and phase correcting meansfor both said paths.

7. In an electrical network adapted to repeat current variations ofvoice frequencies, said network having input and output circuits, anelectron relay amplifier and a gain reducer interposed between saidcircuits, phase changing means connected to the input circuit, meansforming two shunt paths connected between said phase changing means andthe output circuit for repeating current variations, one of said shuntpaths including in series relationship an electron relay amplifier,capacitance capable of passing bass frequencies, capacitance shunted byresistance, and a variable resistor, and the other of said pathsincluding in series relationship a third electron relay amplifier,capacitance serving to pass principally treble frequencies, and avariable series resistor.

8. A method of utilizing an electrical network for repeating voicefrequencies, the network being characterized by three shunt pathsbetween its input and output circuits for repeating current variations,said method comprising effecting a relatively low normal gain thru oneof said paths for frequencies over the entire voice range, and effectingdif ferent gains thru the other of said paths for bass and treblefrequencies.

9. A method of utilizing an electrical network for repeating voicefrequencies, the network being characterized by three shunt pathsbetween its input and output circuits for repeating current variations,said method comprising effecting a relatively low normal gain thru oneof said paths for frequencies over the entire voice range, causing theother two paths to discriminate respectively as to treble and bassfrequencies, and varying the impedances of said other two paths toadjust their respective gains.

In testimony whereof I have hereunto set my hand this 15th day ofOctober, 1930.

MAXIMO AGUIRRE.

